Knife switch with particularly shaped contact blade

ABSTRACT

An edge of a free end portion of the contact blade facing the jaw members of the knife switch has a cutaway portion positioned toward the pivot axis of the blade from the free end of the blade. An outer side edge of the cutaway portion is chamfered and defines one side of an outer nose portion of the blade. The nose portion has a chamfered leading edge disposed at an acute angle with respect to the free end face of the blade.

United States Patent Charles Franklin Latter Inventor Brampton, Ontario,Canada Appl. No. 776,102 Filed Nov. 15, 1968 Patented Mar. 2, 1971Assignee Square D Company Canada Limited Toronto, Ontario, CanadaPriority Mar. 20, 1968 Canada 015,367

KNIFE SWITCH WITH PARTICULARLY SHAPED CONTACT BLADE 3 Claims, 4 DrawingFigs.

US. Cl 200/162, 200/166, 200/144 Int. Cl H0lh 1/42, l-IOlh 21/54 Fieldof Search 200/162, 166 (E), 166 (B)8, 15, 146 (Cursory), 144 (Cursory)200/162 ZOO/162 200/166(E) ABSTRACT: An edge of a free end portion ofthe contact blade facing the jaw members of the knife switch has acutaway portion positioned toward the pivot axis of the blade from thefree end of the blade. An outer side edge of the cutaway portion ischamfered and defines one side of an outer nose portion of the blade.The nose portion has a chamfered leading edge disposed at an acute anglewith respect to the free end face of the blade.

PATENTEUIAR 2mm 25 in/5mm CHARLES F LATTER KNIFE SWITCH WITHPARTICULARLY SHAPED CONTACT BLADE This invention relates to electricswitches of the knife-blade type, and more particularly to the shape ofthe free end portion of a pivoted blade of a knife switch and-itscooperative relation with a stationary jaw member comprising a pair ofcontact jaws.

Most prior knife-switchblades and their cooperating stationary contactjaw members have been designed without giving special consideration tothe region or area of contact as the blade enters or is withdrawn frombetween the contact jaws of the jaw member. Generally, both the bladeand the contact jaws are of simple rectangular configuration and theblade enters and is withdrawn from the contact jaws at the outer cornerportions thereof nearer the pivot axis of the blade.

The switch blade of the present invention is so shaped that the roots ofmost arcs that form as the blade is withdrawn from the contact jaws arerespectively on the free end face of the blade and the side edges of thecontact jaws remote from the pivot axis of the blade, and are not on theedges of the jaws and blade that face each other. This result isobtained because the marginal portion of the blade near the edge whichfaces the jaw members, when the blade is spaced slightly therefrom, hasa cutaway portion positioned inwardly from the free end face of theblade and disposed above the outer portions of the contact jaws at thesides thereof nearer the pivot axis of the blade, and the outer edge ofthe cutaway portion extends toward the jaw members beyond the plane ofthe side edge of the blade to define an outer nose portion which facesthe jaw members and has a leading edge forming an acute angle withrespect to the outer end face of the blade. The pivot axis of the bladeis so positioned with respect to the jaw member and the nose portion isso shaped and is so spaced from the pivot axis that, upon swingingmovement of the blade to its closed position, the leading edge of thenose portion is parallel to the upper face of the jaw member as the noseportion enters between the jaws at a portion thereof remote from thepivot axis of the blade.

It has been found that less are erosion and beading occurs in the use ofswitches made in accordance with this invention than occurs in the useof conventional knife switches. This reduction in arc erosion andbeading results in a switch of longer life and one that requires lessforce for operation during its life. Because the last area of contactbetween the blade and the contact jam member upon withdrawal of theblade is farthest from the pivot axis, the speed of separation isinherently a maximum and the arc is always started in this area. Theheat generated by the arc causes it to rise and its roots to move awayfrom the area of last separation. The edge of the blade at the area ofentry and withdrawal is chamfered, and the entry force is distributedalong the chamfered edges. Since very little arcing takes place in thisarea, the wear is minimal and the life of the switch thereby extended.

It is an object of this invention to provide a knife-switch blade havingits free end portion uniquely shaped to control arcing between the bladeand a cooperating jaw member.

Another object is to provide a knife-switch blade provided with a recessand extending relatively narrow nose portion near the outer end thereofso that the nose portion is withdrawn from between the jaws of acooperating jaw member at an area thereof most remote from a pivot axisof the blade and after a principal contact portion of the blade has beenwithdrawn.

Other objects and advantages of this invention will become apparent fromthe following description wherein reference is made to the drawings, inwhich:

FIG. 1 is a side view of a knife switch in accordance with thisinvention;

FIG. 2 is a view of the knife switch looking from the right in FIG. 1;

FIG. 3 is an enlarged view of the free end portion of a knifeswitchblade shown in FIG. 1; and

FIG. 4 is a view looking from the bottom of FIG. 3.

Referring to the drawing, there is shown a-knife switch having aninsulating base plate 10 carrying a pair of spaced terminal member 11and 12. Mounted on the terminal member 11 is a conventional bifurcatedswitch blade support 14 between the legs of which is pivoted, at one endportion, a generally flat, elongated knife blade 15 by means of a pivotshaft 16. Carried by the other terminal member 12 is a conventionalstationary contact jaw member 17 defined by a metal frame having a baseportion 19, spaced leg portions 20, and inturned and juxtaposed contactjaw portions 21 between which a free end portion of the blade 15 is tobe received and which are biased together by the resiliencey of themetal frame and by a delta-shaped spring member 22. In operation, anoperator means 23 is moved to cause the blade 15 to swing about thepivot shaft 16 for entry of its free end portion between the inturnedcontact jaw portions 21 of the jaw member 17 and withdrawal therefrom.

In accordance with this invention the blade 15 includes a straightlongitudinal edge 24 facing the jaw member 17, extending generallyparallel to the length of the blade from the mounted end portion towardthe free end portion, and disposed in a reference plane perpendicular toopposed flat sides of the blade. The blade 15 has a cutaway portion 25positioned inwardly from a free end face 26 thereof and disposed abovethe upper extremities of the jaw member 17 at the side thereof nearerthe pivot shaft 16 when the blade 15 is in the solid-line position ofFIG. 1. The cutaway portion 25 is defined by an inner sloping edge 28, atop edge 29 parallel with the edge 24, and an outer sloping edge 30. Theouter edge 30 forms an obtuse angle with the top edge 29 and extendsbeyond the reference plane of the edge 24 to define, with a leading edge32 and the end face 26 of the blade 15, an outer nose portion 31. Thecutaway portion 25 and the nose portion 31 are thus disposed on oppositesides of the reference plane of the edge 24. The leading edge 32 ispreferably less than one-half the width of the jaw portions 21 and is atan acute angle with respect to the outer end face 26.

The pivot shaft 16 for the blade 15 is so positioned with respect to thejaw member 17, and the nose portion 31 is so spaced from the pivot shaft16, that upon swinging movement of the blade 15 toward its closedposition, the leading edge 32 is substantially parallel to the upperface of the jaw member 17 as the nose portion 31 enters between the jawportions 21, and the entry is at a relatively narrow region of the jawportions remote from the pivot shaft 16. The completely insertedposition of the blade 15 with respect to the jaw member 17 is shown inbroken lines in FIG. 1.

Upon withdrawal of the blade 15 from between the jaw portions 21 of thejaw member 17 under load, the top edge 29 of the cutaway portion 25 anda portion of the side edge 30 adjacent the top edge separate from thejaw member 17 first, but no arc is formed because current continues toflow through the nose portion 31. As the nose portion 31 separates fromthe jaw member 17, an are indicated at 34 forms, rises from the heat inthe normal position of the switch, and one of its roots moves along theend face 26 of the blade 15 and the other of its roots moves along outerside edges 35 of the jaw portions 21.

The blade 15 is chamfered equally on both sides along the I I top edge29 of the cutaway portion 25 as indicated at 29a, along the edge 30 asindicated at 30a, and to a greater extent along the leading edge 32 asindicated at 32a. The chamfering facilitates entry of the blade betweenthe jaw portions 21.

A U-shaped rigid sheet of insulating material 38 may be placed aroundthe jaw member 17 with the inner surface of its bight portion 38a facingthe outer side edges 35 of the jawportions 12, and its legs 38b and 380on opposite side of the jaw member 17. I 7

Although the invention has been described as incorporated in asingle-pole knife switch, it is apparent that it can be incorporated inmultiple switches with the same advantages.

lclajm: 1. An electric knife switch comprising a stationary contact jawmember, and a generally flat elongated movable contact blade mounted atone end portion for edgewise pivotal movement selectively in onedirection to move a free other end portion into engagement with the jawmember and in an opposite direction to disengage the free end portionfrom the jaw member, the blade having a straight longitudinal edgefacing the jaw member, extending generally parallel to the length of theblade from the mounted end portion toward the free end portion, anddisposed in a reference plane perpendicular to between the straightlongitudinal edge and the projecting nose portion and forming a recessin the blade on the opposite side of the reference plane from theprojecting nose portion.

2. An electric knife switch as claimed in claim 1 wherein the projectingnose portion has a straight leading edge which is parallel to afirst-engaged portion of the jaw member for initial line contacttherewith as the blade is moved into engagement with the jaw member.

3. An electric knife switch as claimed in claim 1 characterized in thata U-shaped sheet of insulating material is positioned adjacent the jawmember and has the inner surface of its bight portion spaced from andfacing the side edges of the jaw member facing away from the mounted endportion of the blade and its leg portions spaced from and disposedrespectively on opposite sides of the jaw member and extending towardthe mounted end portion of the blade.

1. An electric knife switch comprising a stationary contact jaw member,and a generally flat elongated movable contact blade mounted at one endportion for edgewise pivotal movement selectively in one direction tomove a free other end portion into engagement with the jaw member and inan opposite direction to disengage the free end portion from the jawmember, the blade having a straight longitudinal edge facing the jawmember, extending generally parallel to the length of the blade from themounted end portion toward the free end portion, and disposed in areference plane perpendicular to the blade, the free end portion of theblade having a projecting nose portion disposed on the side of thereference plane facing the jaw member and engageable with the jaw memberat a further end thereof from the mounted end portion of the blade, andthe blade having a cutaway portion disposed between the straightlongitudinal edge and the projecting nose portion and forming a recessin the blade on the opposite side of the reference plane from theprojecting nose portion.
 2. An electric knife switch as claimed in claim1 wherein the projecting nose portion has a straight leading edge whichis parallel to a first-engaged portion of the jaw member for initialline contact therewith as the blade is moved into engagement with thejaw member.
 3. An electric knife switch as claimed in claim 1characterized in that a U-shaped sheet of insulating material ispositioned adjacent the jaw member and has the inner surface of itsbight portion spaced from and facing the side edges of the jaw memberfacing away from the mounted end portion of the blade and its legportions spaced from and disposed respectively on opposite sides of thejaw member and extending toward the mounted end portion of the blade.